Inclosed fuse



- R, c. COLE.

mcLosEnfusL APPLICATION FILED APR-2. |920.

1,400,661. nimma Inu-20, 1921.

UNITED STATES PATENT lOFFICE.

ROBERT C. COLE, OF HARTFORD, CONNECTICUT, ASSGNOR TO THE JOHNS-PRATT COMPANY, OF HARTFORD, CONNECTICUT, A STATUTE CORPORATION OF CON- NECTICUT.

INCLOSED FUSE.

Specification of Letters Patent.

Patented Dec. 20, 1921.

Application med April 2, 192e. serial No. 370,637.

To aZZ whom z't mag/concern.'

' Be it known that I, ROBERT C. COLE, citizen of the United States, residing at Hartford, in the county of Hartford and State of Connecticut, have invented a new and useful Improvement in Inclosed Fuses, of which the following is a specication.

'llhisA invention relates to renewable inclosed electric fuses of the knife blade con-v tact'type cartridge class and metal to metal closure species.

These devices are provided to protect apparatus connected in, and substances adjacent tn the circuits. To effect protection the fusible elements must open the circuits under Iexact predetermined conditions of overload and short circuit without endangering surrounding objects or injury to thepermanent elements of the fuses. To insure functioning as safety devices under all conditions the practical ,and commercial requirements as todimensions, strength, carrying capacity, temperature rise, time of safe vcarrying of excess currents and opening of the fusible conductor when the factor of safety is exceeded, and internal pressure and expulsion of gas when the renewable elements fuse, are exacting. These necessitate 'careful selection and relations of the materials forming the permanent and fusible elements and also such provision for the re- -lief of internal pressure resulting froln the transformation of the fusible metal from solid t0 gas as will eliminate explosion, or burning of the parts, or expulsion of dangerous flame. If no vent or an inadequate escape is provided for the as pressure the permanent elements are lia le to be irreparably damaged when the fusible element melts. 'If the vent is too free, flames dangerous to surrounding objects are projected and there is also liability of injury to permanent parts of the fuses.

rlhe amount of metal fused, however, is considerably .reduced if there is suicient internal pressure 4to suppress the arc occurring at the time of fusing. Ideal action 1results when the elements are so constructed and related and the Vents for the gas are so proportioned that only sufficient internalv pressure accrues to suppress the arc, for

then but a minimum amount of metal is vaporized. This is best efected by designing the gas paths so that the gas generatedv is conducted through tortuous passages, the

sizes of which can be definitely'fixed, over and about large areas of aV substantial amount of metal and permitted to escape through slight apertures which in the aggregate have relatively large cross-sectional areas, so that the gas is quite free to escape but by the time it reaches the outer air is chilled below the danger point. This enables all ca acities of fuses of this character t0 be manu actured in large quantities within the prescribed standard limits and sufliciently durable to resist all of the destructive factors and yet operate according to the most exacting requirements.

The object of this invention is to construct a safety'device of the class and type mentioned which will attain the above specified ends. Y

Figure 1 of the accompanying drawings shows a side view 0f a knife blade cartridge fuse with a portion of the casing cut away to show the fusible conductor which is of the character of the well known drop-out link. Fig. 2 shows a section of one end of the casing of the fuse andthe connected parts. Fig. 3 shows a similar section of the same parts rotated ninety degrees. Fig. 4 shows an end view of the fuse. Fig. 5

ybaflie plate in section.

The casing l of the embodiment of the invention illustrated is a tubular piece of the usual insulating material. Screwed `into or otherwise secured in each end of the casing shown is a metallic ferrule 2 that has an exterior thread on its outer. end. Each'terminal, usually of copper, has an outer blade 3 for engagement with the spring plates of the common circuit terminals and an integral inner lug-4 to which an end of the element -5 of ordinary fusible metal is secured by bolt 6. ,The fusible link has two rduced sections 7 so that it will fuse rst at preferred it'isnot an essential ature of the invention.

Secured tightly oneach terminal is a circular baffle plate \8 which is but slightly smaller in diameter than the interior diameter of the ferrule in which it is located. The balile plate is fitted to the terminal s0 tightly that no gas can pass through the jolnt between the terminal and baille plate, but it fits in the ferrule loosely so that there is a slight opening between its outer edge and the interior wall lof the ferrule through which gas can pass. In the outer edge ofeach ferrule, on diametrically oppositesides, are slots 9, and in the edges ofthe terminal and formed in part by the terminal. and in part by the outer face of the bafIie plate are notches 10. lSemi-circular keyI plates 1l with slots 12 shaped to t into land about the notches in the edges of the terminal'blade are slipped onto each blade from opposite sides until they meet and form a circular disky that fits closely and substantially gas tight to the inner end of the blade of the terminal and 'against the outer face of the bale late and end of the ferrule. These i,

key p ates are provided with pins 18 that extend inward when the key plates are in lockin position and enter the notches in theen of the ferrule. The key plates are provided on one face with grooves 14; that lead from the outer circular edge inward\ to the edges ofthe slots that fit the terminal blade. The Inumber and size of theseA grooves can be proportioned to permit just the correct amount of gas to escape through them. Fitted loosely on each terminal blade outside the locking plates is a circular metal cap plate 15, and screwed onto each ferrule is a cap 1.6 which at its outer edge has a flange 17 that when the cap is screwed tightly on the ferrule causes lthe cap plate to press the locking plates tightly against the end of the ferrule. With the parts thus secured the locking plates prevent the rotationof and' also any endwise movement of the terminals. The outer yface of the cap plate fits closely against the inner face of the flange on the cap so thatthere can be no.' leakage of gas between these surfaces, and the diameter of the locking plates when put together is slightly lessthan the interior diameter of the ca'p.

\ To assemble the fuse the terminals provided with the baiiie plates and connected by the fusible element are inserted into the casing with the baie plates lying just inside of the ends of the ferrules which they loosely lit. The locking plates are then inserted into the notches between the inner ends of the blades and the baie plates with the pins projecting into the slotsI in the vends of the ferrules. The cap plates are then slipped on the blades and finally the caps are placed over the cap plates and locking plates and screwed onto the ferrules. l

When gas pressure is generated in the slots in the cap plates and the surfaces of the blades'.

These passages for the escape ofv gas and relief lof internal pressure are free and yet small (being shown exaggerated' in the drawings) and tortuous. Theyconduct the gas outward a long distance over a considerable' area of'a substantial mass of metal and then let it escapel through the spaces between the cap plates and the blades, which spaces while very thin havea total cross-sectional area which provides a sufiicient yet widely distributed vent for the gas. While traversing these tortuous passages vthe hot gas is exposed to the cooling and condensing effect ofa considerable amount of cold metal and is chilled and condensed before it reaches' the outer atmosphere to-a degree far below that which is dangerous to' objects in the vicinity. With these tortuous, yet free aths, afixed relatively low pressure can obtained for a sufficient interval of time tov accelerate the breaking down of the softened metal of the fusible element so that, particularly with the drop-out type of link, but a small amount of metal is fused, and consequently the internal pressure is never abnormally high, for of course the smaller the amount-of metal vaporized the less the internal pressure.

The details of construction of this safety device may be changed, as apparentto those skilled in this art, without departing fromv the invention.

The invention claimed is:

1. -A fuse having an insulating casing, a metallic ferrule secured in one end of the casing, a cap screwed on the ferrule, a termia cap plate loosely fitting theterminal withinl the cap, a baffle plate secured tightly to the tachable locking plates resting against the end-of the ferrule between the cap plate and baille plate and closely fitting the terminal and loosely fitting the cap, and means permitting the passage of gas from the interior tothe exterior of the fuse about the edge of the baiil'e plate, around the edges of the locking plates, betweenthe locking plates and cap plate, and lout between the cap plate and terminal. 1 j

2. A fuse having an insulating casing, a metallic ferrule .secured in one end of the casing, 'a cap screwed on the ferrule, a .termi- 'terminal within the end of the ferrule, de-

- nal extending through the ferrule a-nd cap,

- loc a cap plate within the cap loosely fitting the terminal and closely fitt'ng the cap, a baiile plate secured tightly to the terminal and loosely fitting within the end ot' the ferrule, and detachable locking plates resting against the end of the ferrule between the cap plate and baiiie plate, said locking plates closely fitting and holding the terminal from rotary and longitudinal movements and loosely fittinglthe cap, with'a gas assage betweenv the 'ng lates and cap p ate.

8. A se having an insulating casing, a metallic ferrule secured in one end of the casing, a cap screwed on the ferrule, a terminal extending through the ferrule and ca p, a4 cap plate loosely fitting t-he terminal .within the cap, a baffle plate secured tightly to the terminal within the endJ of the ferrule, and detachable semi-circular lockingD lates resting against the end of the ferru e between the cap plate and baiiie plate,v said loclu'ng lates' closely fitting the terminal and loosely ttingthe cap, and having grooves in the surfaces next to the cap plate.

4. A fuse having an insulating casing, a metallic ferrule secured in one end of the casing, a cap screwed on the ferrule, a terminal extending throu h the ferrule and cap, a vcap plate loosely tting the terminal and closely fitting within the cap, a baille plate secured ti htly to the terminal and loosely fitting wit in the end of the ferrule, and detachable semi-circular locking plates restingA cured in one end of the casing, a cap screwed on the ferrule, a terminal extending through the ferrule and cap,`a cap plate loosely titting the terminal and closely fitting within the cap, a baffle plate secured tightly to the terminal and loosely fitting within the end of the ferrule, detachable semi-circular locking plates with pins extending into the slots in the ferrule, located between the cap plate and baffle plate2 said locking plates closely fitting and holding the terminal from rotary and longitudinal movements, and loosely fitting the cap, with gas channels formed between the locking plates and the cap plate from their outer edges to the termina ROBERT C. COLE. 

